Inconsistent caregivers from an agency; I just do not know what to do anymore.

I think that what you are looking at might hold true for any agency. This is the way of it. You may actually be looking at a necessity for placement at some point. Otherwise negotiating this cycling of care employees will be a given anywhere you go, I think. I am so sorry it is so tough now.

I used Concierage Care at my dad's home and although I spot checked frequently only one had to be dismissed. The others were amazing.
I highly suggest getting a camera system installed to monitor his care.
Tell the scheduler you want the same team every week and ask for those experienced with dementia. We used agency help for daytime and private sitters for evening. Many churches have people who are caregivers. You need help!

I agree with CWillie. You need another layer of help. Find a home health company that has a hospice segment. Then if he doesn’t qualify now (although he should) you will still have a layer of help. I don’t know what I would have done without them for my mom or now with our aunt.
i get upset with myself for not wanting to change when things are not where they should be. It’s like instead of assigning you their best more experienced workers they take advantage of your willingness to accept who they send you as you’ve been with them so long. . 40 is truly excessive. I can’t imagine.
I hope you find someone soon who truly wants to help him and you.

I think I would definitely try a different company, but maybe consider supplementing that with a person you hire privately so that you have at least some consistency. I also think it may be time to look into hospice, even though you say he is still eating at 86 lbs he is clearly fading away.